"Bro, CLEARLY this is a sign from the gods to build our capital in a swamp!"

I think I would make a disservice to history by trying to summarize it, so I just bluntly copied from this link: “Based on these codices as well as other histories, it appears that the Mexicas arrived at Chapultepec in or around the year 1248.

At the time of their arrival, the Valley of Mexico contained many city-states, the most powerful of which were Culhuacan to the south, and Azcapotzalco to the west. The Tepanecs of Azcapotzalco soon expelled the Mexicas from Chapultepec. In 1299, Culhuacan ruler Cocoxtli gave them permission to settle in the empty barrens of Tizapan, where they were eventually assimilated into Culhuacan culture.

In 1323, the Mexica asked the new ruler of Culhuacan, Achicometl, for his daughter, in order to make her the goddess Yaocihuatl. Unbeknownst to the king, the Mexicas actually planned to sacrifice her. As the story goes, during a festival dinner, a priest came out wearing her flayed skin as part of the ritual. Upon seeing this, the king and the people of Culhuacan were horrified and expelled the Mexicas.

According to Aztec legend, the Aztecs were shown a vision of an eagle perched on a prickly pear cactus, clutching a snake in its talons. This vision indicated that this was the location where they were to build their home. In any event, the Aztecs eventually arrived on a small swampy island in Lake Texcoco where they founded the town of Tenochtitlan in 1325. In 1376, the Mexicas elected their first Huey Tlatoani, Acamapichtli, who was living in Texcoco at the time.”

Note to extend this: The Mexicas were basically banished to the worse place possible, which lacked food, was full of venomous snakes and they were exposed to attacks in a mud-like barren land.

In fact, the snake has a direct relationship to the harsh realities of their banishment (basically venomous snakes) and how they conquered over that land (Tenochtiltlan, the Venice of America).

By flaying. It was a radical new idea at the time.